High-performance suspension capacitor H-bridge cascade multi-level inverter

Abstract

The invention discloses a high-performance suspension capacitor H-bridge cascade multi-level inverter. The inverter comprises an H-bridge inversion unit, a suspension capacitor inversion unit, an output filter inductor L1 and an output filter capacitor C1. The H-bridge inverter unit is a bridge circuit formed by connecting four switching tubes Q11, Q12, Q13 and Q14, and the input side of the H-bridge inverter unit is connected with a direct-current voltage source Vdc; the suspension capacitor inversion unit is a bridge circuit formed by connecting four switching tubes Q21, Q22, Q23 and Q24 and a suspension capacitor C, the input side is connected with the output side of the H-bridge inversion unit, and the output side is connected with a load through an output filter inductor L1 and an output filter capacitor C1. The beneficial effects of the invention are that the device number is small, the structure is simple, the switching frequency is high, and the application range is wide; the problem of output overmodulation of the inverter is solved, and the switching frequency of the H-bridge inverter unit is reduced; the control of the suspension capacitor voltage in different working modes is realized; and the double-frequency voltage ripples on the direct current side and the low-order harmonic content generated by the output alternating current voltage are reduced.

Description

Technical Field

[0001] The present application relates to the field of electronic energy storage, and in particular to a high-performance suspended capacitor H-bridge cascade multi-level inverter. Background Art

[0002] In order to transform the traditional energy industry to green and low-carbon, in the field of new energy power generation, we should continue to develop wind power generation and photovoltaic power generation to ensure the steady and rapid development of new energy power generation. While developing centralized power generation, we should promote the research of distributed power generation, always implement the basic principle of common development of the two, continue to study and actively promote new energy power generation technology, and promote the application and development of wind and photovoltaic power generation; in the field of energy storage, develop new energy storage to improve the regulation capacity, comprehensive efficiency and safety guarantee of energy and power systems, and at the same time promote the research on the smooth, safe and stable operation of energy storage systems in various operation modes, such as single machine, parallel, grid-connected, island and grid-connected modes, to achieve flexible energy scheduling and support the construction of new power systems. Inverters, as the core part of power conversion in the above fields, help improve power quality and promote the development of green energy, and are widely studied. The traditional two-level inverter has a simple structure and is easy to control, but the output current and output voltage of the inverter are affected by the number of inverter output levels, and the harmonic content is high. It is necessary to increase the switching frequency of the power device and increase the filter parameter value, but the high switching frequency will increase the switching loss accordingly, and the large filter parameter will increase the system volume and cost.

[0003] Since the input power of the single-phase inverter is DC and the output power is AC, there is a double frequency power fluctuation in the circuit, resulting in a double frequency voltage fluctuation on the DC side. When the double frequency voltage fluctuation is large, it will increase the low-order harmonics of the inverter output voltage, which is not easy to filter. In addition, the increase in DC side voltage fluctuation will increase circuit losses. Therefore, in order to ensure the normal operation of the single-phase inverter, the suppression of double frequency power fluctuation should be considered. Usually, the double frequency voltage fluctuation on the DC side can be suppressed by increasing the value of the input terminal capacitor, but it will cause the system dynamic response to slow down and the inverter size and cost to increase. Considering that increasing the capacitance will reduce the power density of the circuit and reduce the efficiency of the inverter, many other methods have been studied to suppress the double frequency voltage fluctuation on the DC side, mainly adding a double frequency power decoupling circuit, optimizing the control strategy, etc.

[0004] Traditional two-level inverters have shortcomings such as small number of output voltage levels, large filtering parameters, low equivalent switching frequency, and high voltage stress of power devices. In traditional high-frequency modulation strategies, carrier stacking and carrier phase shift modulation cannot take into account the problems of total harmonic distortion of output voltage and suspension capacitor voltage control. In order to reduce switching losses, the traditional hybrid modulation strategy is adopted to make the H-bridge inverter unit switch tube operate at the base frequency and the suspension capacitor inverter unit switch tube operate at a high switching frequency, which will cause over-modulation and suspension capacitor voltage out of control. The output power of the single-phase inverter contains double frequency power fluctuations, and a large-capacity capacitor is required for filtering on the DC side. Summary of the invention

[0005] The present application is a high-performance suspended capacitor H-bridge cascade multi-level inverter designed to solve the above technical problems.

[0006] The technical solution adopted by this application to solve its technical problem is:

[0007] A high-performance suspended capacitor H-bridge cascade multi-level inverter, the inverter includes an H-bridge inverter unit, a suspended capacitor inverter unit, an output filter inductor L1 and an output filter capacitor C1; the H-bridge inverter unit consists of four switch tubes Q 11 , Q 12 , Q 13 and Q 14 Connected into a bridge circuit, the input side of which is connected to a DC voltage source V dc The floating capacitor inverter unit consists of 4 switch tubes Q 21 , Q 22 , Q 23 , Q 24 The circuit is connected to the suspension capacitor C to form a bridge circuit, the input side of which is connected to the output side of the H-bridge inverter unit, and the output side of which is connected to the load through the output filter inductor L1 and the output filter capacitor C1.

[0008] The high-performance suspended capacitor H-bridge cascade multi-level inverter, the suspended capacitor C is located between the DC and AC sides of the suspended capacitor inverter unit, and can be used to buffer the fluctuating power and bear a certain voltage ripple; the voltage value of the suspended capacitor C is V c is the DC voltage source V dc Half the voltage value.

[0009] The high-performance floating capacitor H-bridge cascade multi-level inverter has multiple conduction modes, and 8 working modes are formed by different conduction modes. The 8 working modes are:

[0010] The working modes when the positive half cycle outputs 2E, E, 0 include working modes 1-4:

[0011] Working mode 1: The floating capacitor H-bridge cascade multi-level inverter outputs 2E level; at this time, the H-bridge inverter unit switch tube Q 11 , Q 14 When the H-bridge inverter unit is turned on, it outputs 2E level; when the floating inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 21 , Q 22 When it is turned on, the floating capacitor inverter unit outputs 0 level, and the capacitor is neither charged nor discharged;

[0012] Working mode 2: The suspended capacitor H-bridge cascade multi-level inverter outputs E level; at this time, the H-bridge inverter unit switch tube Q 11 , Q 14 The H-bridge inverter unit outputs 2E level; the switch tube Q of the floating inverter unit 22 , Q 23 When the inverter is turned on, the inverter unit outputs -E level. When the inverter output current direction is positive, the capacitor is charged, and when the inverter output current direction is negative, the capacitor is discharged.

[0013] Working mode 3: The suspended capacitor H-bridge cascade multi-level inverter outputs E level; when the H-bridge inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 11 , Q 12 The H-bridge inverter unit outputs 0 level; the suspended inverter unit outputs E level, and the switch tube Q of the suspended inverter unit 21 , Q 24 When the inverter output current is positive, the capacitor is discharged, and when the inverter output current is negative, the capacitor is charged;

[0014] Working mode 4: The suspended capacitor H-bridge cascade multi-level inverter outputs 0 level; both the H-bridge inverter unit and the suspended inverter unit output 0 level. In this working mode, the switch tube of the H-bridge inverter unit is Q 11 , Q 12 Conducting, suspending the inverter unit switch tube Q 21 , Q 22 When conducting, the capacitor neither charges nor discharges;

[0015] The working modes when the negative half cycle outputs 2E, E, 0 include working modes 5-8:

[0016] Working mode 5: The suspended capacitor H-bridge cascade multi-level inverter outputs -2E level; at this time, the H-bridge inverter unit switch tube Q 12 , Q 13 When the H-bridge inverter unit is turned on, it outputs -2E level; when the floating inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 23 , Q24 When it is turned on, the floating capacitor inverter unit outputs 0 level, and the capacitor is neither charged nor discharged;

[0017] Working mode 6: The suspended capacitor H-bridge cascade multi-level inverter outputs E level; at this time, the H-bridge inverter unit switch tube Q 12 , Q 13 The H-bridge inverter unit outputs -2E level; the switch tube Q of the floating inverter unit 21 , Q 24 When the inverter is turned on, the suspended inverter unit outputs the E level. When the inverter output current direction is positive, the capacitor is charged, and when the inverter output current direction is negative, the capacitor is discharged.

[0018] Working mode 7: Suspended capacitor H-bridge cascade multi-level inverter outputs -E level; when the H-bridge inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 13 , Q 14 The H-bridge inverter unit outputs 0 level; the suspended inverter unit outputs -E level, and the switch tube Q of the suspended inverter unit 22 , Q 23 When the inverter output current is positive, the capacitor is discharged, and when the inverter output current is negative, the capacitor is charged;

[0019] Working mode 8: The suspended capacitor H-bridge cascade multi-level inverter outputs 0 level; both the H-bridge inverter unit and the suspended inverter unit output 0 level. In this working mode, the switch tube of the H-bridge inverter unit is Q 13 , Q 14 Conducting, suspending the inverter unit switch tube Q 23 , Q 24 When it is on, the capacitor neither charges nor discharges.

[0020] The high-performance suspended capacitor H-bridge cascade multi-level inverter also includes a mixed frequency modulation strategy based on modulation wave decomposition. The strategy targets the E-level overmodulation situation, increases the modulation process in this interval, decomposes the modulation wave of the suspended capacitor inverter unit that exceeds the carrier, and adjusts the modulation wave of the overmodulated part of the H-bridge inverter unit and the suspended capacitor inverter unit, so that the H-bridge inverter unit outputs 2E, 0 levels, and the suspended capacitor unit outputs -E, E levels, thereby achieving normal E-level output.

[0021] The high-performance suspended capacitor H-bridge cascade multi-level inverter and the hybrid frequency modulation strategy based on modulation wave decomposition work in a specific manner as follows: the H-bridge inverter unit works at a high frequency in the decomposed interval using a single-polarity frequency-multiplied modulation method with modulation wave inversion, and the switch tube Q 11 and Q 12 Using a modulated wave signal with equal amplitude but 180° phase difference, vref1- is the inverted modulation wave. In any carrier cycle, the switch tube Q 11 and Q 12 The modulated wave signal and the carrier have two intersection points: when v ref1 ≥U cH When the drive switch tube Q 11 On, on the contrary Q 13 When V ref1- ≥U cH When the drive switch tube Q 12 On, on the contrary Q 14 Conductivity.

[0022] The high-performance suspended capacitor H-bridge cascade multi-level inverter and the hybrid frequency modulation strategy based on modulation wave decomposition work in the following way: the suspended capacitor inverter unit adopts single polarity frequency multiplication modulation in all intervals, and the switch tube Q 21 and Q 22 The modulated wave signal v is equal in amplitude but 180° in phase. ref2 and v ref2- ; When the sine wave v ref >0, Q 11 is high level, and low level at other times; when u m >u c2 When 12 is low level, and Q 12 is high level. m >u c1 When 21 is high level, and Q 21 is low level; when u m >u c2 When 22 is high level, and Q 22 is a low level; the modulation wave output voltage waveform of the suspended capacitor inverter unit after the modulation wave is decomposed is v2'.

[0023] The high-performance suspended capacitor H-bridge cascade multi-level inverter further includes a capacitor voltage regulation system control strategy based on working mode switching; the strategy is: by introducing the load end output voltage v o1 , output current i o , floating end capacitor voltage V c and capacitor voltage reference value V c *Perform zero-crossing comparison, and control the output value △V c After the kp link, the output part v', v' and v of the H-bridge inverter unit during high-frequency conversion are obtained. a The given values ​​are added to get the modulation wave v of the H-bridge inverter unit ref1 , modulation wave v ref1The modulation circuit is used to modulate the four switch tubes Q of the floating capacitor inverter unit. 21 , Q 22 , Q 23 , Q 24 Modulate.

[0024] The high-performance suspended capacitor H-bridge cascade multi-level inverter includes a zero-crossing comparison control method, which is: using the current inverter output voltage value u o Subtract the previous voltage value u olast , the difference is compared with the detected inverter output current i o If the polarity of the obtained signal is non-negative, the inverter is controlled to work in working mode 1, otherwise it works in working mode 2;

[0025] The working mode 1 is: when the inverter output voltage passes through the zero point in the positive half cycle, the current value i o ≤0, when p2(t)<0, the floating capacitor inverter unit absorbs active power, i c >0, the DC side floating capacitor of the floating capacitor inverter unit will work in the charging state; when p2(t)>0, the floating capacitor inverter unit outputs active power, i c <0, the DC side floating capacitor of the floating capacitor inverter unit is controlled to work in the discharge state;

[0026] The working mode 2 is: when the inverter output voltage passes through the zero point in the positive half cycle, the current value i o >0, when p2(t)<0, the floating capacitor inverter unit outputs active power, i c <0, the DC side floating capacitor of the floating capacitor inverter unit will work in the discharge state; when p2(t)>0, the floating capacitor inverter unit absorbs active power, i c >0, the DC side floating capacitor of the floating capacitor inverter unit will work in the charging state.

[0027] The high-performance suspended capacitor H-bridge cascade multi-level inverter also includes a third harmonic injection strategy based on a modulation wave decomposition modulation strategy: the control system can configure the proportional coefficient K p The negative feedback of the floating capacitor voltage forms a single closed loop to generate the power switch tube Q 11 , Q 12 , Q 13 , Q 14 , Q 21 , Q 22 , Q 23 , Q 24 PWM pulse signal; after injecting the third harmonic, v r1'Decompose the modulation wave to get the decomposed H-bridge inverter unit modulation wave v r1 and the suspended inverter unit modulated wave v r2 After injecting the third harmonic, the floating capacitor voltage is controlled by changing the active power of the H-bridge inverter unit.

[0028] The high-performance suspended capacitor H-bridge cascade multi-level inverter, the suspended capacitor voltage control method is: using a proportional controller, giving a capacitor voltage reference value V c *, with the actual value of the real-time sampling capacitor voltage V c Difference to get △V c , the duty cycle to be adjusted is obtained through the proportional controller, thereby adjusting the output voltage of the H-bridge inverter unit; when charging, △V c Increase, the floating capacitor inverter unit outputs negative active power to control the floating capacitor voltage charging; conversely, when △V c When it decreases, the suspension capacitor voltage is controlled to discharge; by repeating this process, the actual value of the suspension capacitor voltage can be controlled to tend toward the reference value.

[0029] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0030] (1) The floating capacitor H-bridge cascade multi-level inverter requires a small number of components and has a simple structure. It can achieve a higher switching frequency by using components with a low withstand voltage rating, thus expanding the scope of application.

[0031] (2) In order to realize the operation of the H-bridge inverter unit at a low switching frequency and solve the overmodulation problem of the suspended capacitor inverter unit, a hybrid frequency modulation strategy based on modulation wave decomposition is proposed, which effectively solves the overmodulation problem of the inverter output and reduces the switching frequency of the H-bridge inverter unit.

[0032] (3) In order to achieve stable voltage of the suspended capacitor, a suspended capacitor voltage control strategy is proposed. Based on the active power decomposition control of working mode switching, the control of the suspended capacitor voltage in different working modes is realized.

[0033] (4) In order to solve the problem of increased voltage ripple on the DC side caused by double frequency power fluctuation on the output side of the single-phase inverter, a DC side double frequency power fluctuation suppression scheme is proposed. Without increasing the value of the input side capacitor, the double frequency voltage fluctuation on the DC side is effectively suppressed, solving the problem of high double frequency power pulsation in the suspended capacitor H-bridge cascade multi-level inverter. This scheme effectively reduces the double frequency voltage ripple on the DC side without adding additional circuits, and reduces the low-order harmonic content generated by the output AC voltage due to double frequency power fluctuation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0035] Figure 1 It is the topology diagram of suspended capacitor H-bridge cascade multi-level inverter;

[0036] FIG2(a) is a topological diagram of the operating mode-1 of the suspended capacitor H-bridge cascade multi-level inverter;

[0037] FIG2( b ) is a topological diagram of the operating mode-2 of the suspended capacitor H-bridge cascade multi-level inverter;

[0038] Figure 2(c) is a topological diagram of the operating mode-3 of the suspended capacitor H-bridge cascade multi-level inverter;

[0039] Figure 2(d) is a topology diagram of the operating mode-4 of the suspended capacitor H-bridge cascade multi-level inverter;

[0040] Figure 2(e) is a topology diagram of the operating mode-5 of the suspended capacitor H-bridge cascade multi-level inverter;

[0041] Figure 2(f) is a topological diagram of the operating mode-6 of the suspended capacitor H-bridge cascade multi-level inverter;

[0042] Figure 2(g) is a topological diagram of the operating mode-7 of the suspended capacitor H-bridge cascade multi-level inverter;

[0043] Figure 2(h) is a topological diagram of the operating mode-8 of the suspended capacitor H-bridge cascade multi-level inverter;

[0044] Figure 3(a) shows a hybrid frequency modulation strategy based on modulation wave decomposition. a- When it is greater than the capacitor voltage value E;

[0045] Figure 3(b) shows the hybrid frequency modulation strategy based on modulation wave decomposition. a+ When it is greater than the capacitor voltage value E;

[0046] Figure 4 Flowchart of hybrid frequency modulation strategy based on modulation wave decomposition;

[0047] Figure 5 Decompose the open-loop control diagram for active power;

[0048] Figure 6(a) is a schematic diagram of the influence of complementary areas under different working modes - the complementary area of ​​working mode 1 remains unchanged; Figure 6(b) is a schematic diagram of the influence of complementary areas under different working modes - the complementary area of ​​working mode 1 decreases; Figure 6(c) is a schematic diagram of the influence of complementary areas under different working modes - the complementary area of ​​working mode 1 increases; Figure 6(d) is a schematic diagram of the influence of complementary areas under different working modes - the complementary area of ​​working mode 2 remains unchanged; Figure 6(e) is a schematic diagram of the influence of complementary areas under different working modes - the complementary area of ​​working mode 2 decreases;

[0049] Figure 6(f) is a schematic diagram of the impact of complementary areas under different working modes - working mode 2 has an increase in complementary areas;

[0050] Figure 7 It is a control strategy diagram of the capacitor voltage regulation system based on working mode switching;

[0051] Figure 8 This is the flow chart of the zero-crossing comparison program;

[0052] FIG9( a ) is a working mode diagram of the suspended capacitor inverter unit - charging mode 1;

[0053] FIG9( b ) is a working mode diagram of the suspended capacitor inverter unit - charging mode 2;

[0054] FIG9( c ) is a working mode diagram of the suspended capacitor inverter unit - discharge mode 1;

[0055] FIG9( d ) is a working mode diagram of the suspended capacitor inverter unit - discharge mode 2;

[0056] FIG9( e ) is a working mode diagram of the suspended capacitor inverter unit - neither charging nor discharging mode 1;

[0057] FIG9( f ) is a working mode diagram of the suspended capacitor inverter unit - neither charging nor discharging mode 2;

[0058] FIG10( a ) is a unipolar frequency doubling modulation strategy of two H-bridge units - H-bridge inverter unit modulation diagram;

[0059] Figure 10(b) is a modulation diagram of the unipolar frequency doubling modulation strategy of two H-bridge units - suspended capacitor inverter unit;

[0060] Fig.11 is the relationship diagram between m and k;

[0061] Fig.12 Control strategy diagram for the third harmonic injection strategy. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0063] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0064] In order to facilitate the understanding of the various embodiments of the present application, Figure 1 A high-performance suspended capacitor H-bridge cascade multi-level inverter is shown, the inverter includes an H-bridge inverter unit (also called an H-bridge inverter circuit), a suspended capacitor inverter unit (also called a suspended capacitor H-bridge), an output filter inductor L1 and an output filter capacitor C1; the H-bridge inverter unit consists of four switch tubes Q 11 , Q 12 , Q 13 and Q 14 Connected into a bridge circuit, the input side of which is connected to a DC voltage source V dc The floating capacitor inverter unit consists of 4 switch tubes Q 21 , Q 22 , Q 23 , Q 24 The circuit is connected to the suspension capacitor C to form a bridge circuit, the input side of which is connected to the output side of the H-bridge inverter unit, and the output side of which is connected to the load through the output filter inductor L1 and the output filter capacitor C1.

[0065] The high-performance suspended capacitor H-bridge cascade multi-level inverter, the suspended capacitor C is located between the DC and AC sides of the suspended capacitor inverter unit, and can be used to buffer the fluctuating power and bear a certain voltage ripple; the voltage value of the suspended capacitor C is V c is the DC voltage source V dc Half the voltage value.

[0066] (1) Working principle of inverter

[0067] The high-performance floating capacitor H-bridge cascade multi-level inverter has multiple conduction modes, and 8 working modes are formed by different conduction modes. The 8 working modes are:

[0068] The working modes when the positive half cycle outputs 2E, E, and 0 include working modes 1-4, namely Figure 2(a), Figure 2(b), Figure 2(c), and Figure 2(d).

[0069] Working mode 1: The floating capacitor H-bridge cascade multi-level inverter outputs 2E level; at this time, the H-bridge inverter unit switch tube Q 11, Q 14 When the H-bridge inverter unit is turned on, it outputs 2E level; when the floating inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 21 , Q 22 When it is turned on, the floating capacitor inverter unit outputs 0 level, and the capacitor is neither charged nor discharged;

[0070] Working mode 2: The suspended capacitor H-bridge cascade multi-level inverter outputs E level; at this time, the H-bridge inverter unit switch tube Q 11 , Q 14 The H-bridge inverter unit outputs 2E level; the switch tube Q of the floating inverter unit 22 , Q 23 When the inverter is turned on, the inverter unit outputs -E level. When the inverter output current direction is positive, the capacitor is charged, and when the inverter output current direction is negative, the capacitor is discharged.

[0071] Working mode 3: The suspended capacitor H-bridge cascade multi-level inverter outputs E level; when the H-bridge inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 11 , Q 12 The H-bridge inverter unit outputs 0 level; the suspended inverter unit outputs E level, and the switch tube Q of the suspended inverter unit 21 , Q 24 When the inverter output current is positive, the capacitor is discharged, and when the inverter output current is negative, the capacitor is charged;

[0072] Working mode 4: The suspended capacitor H-bridge cascade multi-level inverter outputs 0 level; both the H-bridge inverter unit and the suspended inverter unit output 0 level. In this working mode, the switch tube of the H-bridge inverter unit is Q 11 , Q 12 Conducting, suspending the inverter unit switch tube Q 21 , Q 22 When conducting, the capacitor neither charges nor discharges;

[0073] The working modes when the negative half cycle outputs 2E, E, and 0 include working modes 5-8, namely Figure 2(e), Figure 2(f), Figure 2(g), and Figure 2(h).

[0074] Working mode 5: The suspended capacitor H-bridge cascade multi-level inverter outputs -2E level; at this time, the H-bridge inverter unit switch tube Q 12 , Q 13 When the H-bridge inverter unit is turned on, it outputs -2E level; when the floating inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 23 , Q 24When it is turned on, the floating capacitor inverter unit outputs 0 level, and the capacitor is neither charged nor discharged;

[0075] Working mode 6: The suspended capacitor H-bridge cascade multi-level inverter outputs E level; at this time, the H-bridge inverter unit switch tube Q 12 , Q 13 The H-bridge inverter unit outputs -2E level; the switch tube Q of the floating inverter unit 21 , Q 24 When the inverter is turned on, the suspended inverter unit outputs the E level. When the inverter output current direction is positive, the capacitor is charged, and when the inverter output current direction is negative, the capacitor is discharged.

[0076] Working mode 7: Suspended capacitor H-bridge cascade multi-level inverter outputs -E level; when the H-bridge inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 13 , Q 14 The H-bridge inverter unit outputs 0 level; the suspended inverter unit outputs -E level, and the switch tube Q of the suspended inverter unit 22 , Q 23 When the inverter output current is positive, the capacitor is discharged, and when the inverter output current is negative, the capacitor is charged;

[0077] Working mode 8: The suspended capacitor H-bridge cascade multi-level inverter outputs 0 level; both the H-bridge inverter unit and the suspended inverter unit output 0 level. In this working mode, the switch tube of the H-bridge inverter unit is Q 13 , Q 14 Conducting, suspending the inverter unit switch tube Q 23 , Q 24 When it is on, the capacitor neither charges nor discharges.

[0078] The high-performance suspended capacitor H-bridge cascade multi-level inverter also includes a mixed frequency modulation strategy based on modulation wave decomposition. The strategy targets the E-level overmodulation situation, increases the modulation process in this interval, decomposes the modulation wave of the suspended capacitor inverter unit that exceeds the carrier, and adjusts the modulation wave of the overmodulated part of the H-bridge inverter unit and the suspended capacitor inverter unit, so that the H-bridge inverter unit outputs 2E, 0 levels, and the suspended capacitor unit outputs -E, E levels, thereby achieving normal E-level output.

[0079] From the above analysis, we know that when the output voltage v o =E, there are two corresponding total output state combinations, namely (2E, -E) and (0, E). According to the analysis of the working mode in Figure 2 above, whether the output voltage of the H-bridge inverter unit or the floating capacitor inverter unit is 0, there are two switching action modes. In order to facilitate modulation, when the inverter modulation wave is greater than 0, the H-bridge inverter unit switch tube Q11 And the switch tube Q 12 Conducting, switching tube Q 13 And the switch tube Q 14 Disconnect or suspend the capacitor inverter unit switch tube Q 21 And the switch tube Q 22 Conducting, switching tube Q 23 And the switch tube Q 24 Disconnect; when the inverter modulation wave is less than 0, the H-bridge inverter unit switch tube Q 13 And the switch tube Q 14 Conducting, switching tube Q 11 And the switch tube Q 12 Disconnect or suspend the capacitor inverter unit switch tube Q 23 And the switch tube Q 24 Conducting, switching tube Q 21 And the switch tube Q 22 disconnect.

[0080] Table 1 gives the synthesis method of the inverter output level and lists the switch states corresponding to different output levels. "1" means on and "0" means off. It can be seen from the synthesis method of the 5 levels in the table that when the output voltage of the suspended capacitor H-bridge cascade multi-level inverter is E, the H-bridge inverter unit can output 2E level and the suspended inverter unit outputs -E level, or the H-bridge inverter unit can output 0 level and the suspended inverter unit outputs E level, that is, there are 2 output modes, so in the process of inverter pulse width modulation, there are redundant switch states, and multiple output combinations can be selected. It can be seen from Table 1 that when the number of levels is synthesized, the suspended capacitor voltage control can be achieved according to the charging and discharging state of the suspended capacitor.

[0081] Table 1 Inverter output five-level synthesis method

[0082]

[0083] (2) Hybrid frequency modulation strategy based on modulation wave decomposition

[0084] The high-performance suspended capacitor H-bridge cascade multi-level inverter and the hybrid frequency modulation strategy based on modulation wave decomposition work in a specific manner as follows: the H-bridge inverter unit works at a high frequency in the decomposed interval using a single-polarity frequency-multiplied modulation method with modulation wave inversion, and the switch tube Q 11 and Q 12 Using a modulated wave signal with equal amplitude but 180° phase difference, v ref1- is the inverted modulation wave. In any carrier cycle, the switch tube Q 11 and Q 12 The modulated wave signal and the carrier have two intersection points: when v ref1 ≥U cH When the drive switch tube Q11 On, on the contrary Q 13 When V ref1- ≥U cH When the drive switch tube Q 12 On, on the contrary Q 14 Conductivity.

[0085] The specific principle is shown in Figure 3(a) and (b). In Figure 3(a), U cH , U ch are carriers with the same frequency and a phase difference of 90°, located in the [-2E, 2E] and [-E, E] domains respectively, U cH For H-bridge inverter unit modulation, U ch Used for modulation of suspended capacitor inverter unit; v ref1 , v ref2 They are the modulation waves of the decomposed H-bridge inverter unit and the modulation waves of the suspended capacitor inverter unit. In Figure 3(b), U cH , U ch is a carrier with the same frequency and phase, and the inverter expects the output voltage v o1 is a sinusoidal waveform with an amplitude of V m , the H-bridge inverter unit outputs a rectangular waveform v1, where the H-bridge inverter unit modulation wave and the suspended capacitor inverter unit modulation wave satisfy:

[0086] V m =v ref1 +v ref2 (1)

[0087] Under the proposed strategy, the H-bridge inverter unit operates at high frequency in the decomposed interval using a unipolar frequency-multiplied modulation method with an inverted modulation wave. 11 and Q 12 The modulated wave signal with equal amplitude but 180° phase difference is used, v ref1- is the inverted modulation wave. In any carrier cycle, the switch tube Q 11 and Q 12 The modulated wave signal and the carrier have two intersection points: when v ref1 ≥U cH When the drive switch tube Q 11 On, on the contrary Q 13 When V ref1- ≥U cH When the drive switch tube Q 12 On, on the contrary Q 14 In the figure, the shaded area is the complementary area after subtraction decomposition. The H-bridge inverter unit performs high-frequency conversion in this area, and the output voltage waveform is v1', and the output fundamental wave is still V m .

[0088] The high-performance suspended capacitor H-bridge cascade multi-level inverter and the hybrid frequency modulation strategy based on modulation wave decomposition work in the following way: the suspended capacitor inverter unit adopts single polarity frequency multiplication modulation in all intervals, and the switch tube Q 21 and Q 22 The modulated wave signal v is equal in amplitude but 180° in phase. ref2 and v ref2- ; When the sine wave v ref >0, Q 11 is high level, and low level at other times; when u m >u c2 When 12 is low level, and Q 12 is high level. m >u c1 When 21 is high level, and Q 21 is low level; when u m >u c2 When 22 is high level, and Q 22 is a low level; the modulation wave output voltage waveform of the suspended capacitor inverter unit after the modulation wave is decomposed is v2'.

[0089] From the above analysis, it can be seen that when ωt is in the complementary regions of [α1, α2], [π-α2, π-α1], [π+α1, π+α2], and [2π-α2, 2π-α1], the suspended capacitor inverter unit will be overmodulated. Let the modulation signal H of the overmodulation part before decomposition be:

[0090] H=V m sin(ωt)(2)

[0091] According to the above principle, the modulation strategy flow chart is as follows: Figure 4 As shown in the figure, the modified modulation wave expression for 1 / 4 period is listed, and the expressions for the remaining periods can be derived from the symmetry of the waveform.

[0092] (3) Suspended capacitor voltage control strategy

[0093] The high-performance suspended capacitor H-bridge cascade multi-level inverter further includes a capacitor voltage regulation system control strategy based on working mode switching; the strategy is: by introducing the load end output voltage v o1 , output current i o , floating end capacitor voltage V c and capacitor voltage reference value V c *Perform zero-crossing comparison, and control the output value △V c After the kp link, the output part v', v' and v of the H-bridge inverter unit during high-frequency conversion are obtained.a The given values ​​are added to get the modulation wave v of the H-bridge inverter unit ref1 , modulation wave v ref1 The modulation circuit is used to modulate the four switch tubes Q of the floating capacitor inverter unit. 21 , Q 22 , Q 23 , Q 24 Modulate.

[0094] In order to control the voltage of the floating capacitor, an active power decomposition control strategy is proposed. Based on the above analysis, the expression of the Fourier series v1'(t) of the output voltage waveform of the H-bridge inverter unit is:

[0095] v1'(t)=V m1 sin(ωt)+h n1 (nωt)+v'(t) (3)

[0096] Where V m1 sin(ωt) is the fundamental wave output of the H-bridge inverter unit when it performs industrial frequency conversion, v'(t) is the output of the H-bridge inverter unit when it performs high frequency conversion, h n1 (nωt) is the harmonic part of the H-bridge inverter unit output at this time, and the fundamental wave of the H-bridge inverter unit output is still V m .

[0097] According to the topological working principle, the remaining part of the output voltage is synthesized by the suspended capacitor inverter unit using a high-frequency PWM modulation strategy. Therefore, the expression of the expected voltage v2'(t) of the suspended capacitor inverter unit is:

[0098] v2'(t)=V m sin(ωt)-v1'(t)=-h n (nωt) (4)

[0099] For general cases, assuming that the load power factor angle is θ (θ∈[-π,π]), the output current can be expressed as:

[0100] i o =I m sin(ωt-θ) (5)

[0101] It can be seen from formula (4) that when the bridge arm is lossless, the average output power P2 of the suspended capacitor inverter unit is the average power emitted by the harmonic in one cycle, the average output power of the suspended capacitor inverter unit is 0, and the average output power of the H-bridge inverter unit is equal to the inverter output power, which can be expressed by formula (6).

[0102]

[0103] From equations (3), (4) and (5), we can see that P2 can be expressed as:

[0104]

[0105] Where P'(t) is the active power output corresponding to the H-bridge inverter unit v'(t).

[0106] It can be seen from formula (7) that by adjusting the size of the complementary region v' of the H-bridge inverter unit, the average output power P2 of the floating capacitor inverter unit can be indirectly changed. The specific floating capacitor voltage open-loop control scheme is as follows: Figure 5 According to the working principle of the inverter, when the complementary region v' changes, the H-bridge inverter unit modulates the wave v ref1 will change accordingly, that is, the output active power of the H-bridge inverter unit will change, because v o1 To maintain the inverter output power P o The suspended capacitor inverter unit modulation wave v ref2 The instantaneous active power p2(t) will change accordingly, that is, according to the change of the output power p1(t) of the H-bridge inverter unit, the size of the instantaneous active power p2(t) will be adjusted. When the active power generated in the H-bridge inverter unit is greater than the power transmitted to the load, the remaining power will be transmitted to the suspended capacitor inverter unit, thereby charging the suspended capacitor on the suspended capacitor inverter unit; when the active power generated in the H-bridge inverter unit is less than the power transmitted to the load, the suspended capacitor inverter unit will output active power, thereby discharging the suspended capacitor on the suspended capacitor inverter unit.

[0107] Based on the above principle, a closed-loop control system for suspension capacitor voltage regulation can be designed to adjust the active power control capacitor voltage injected into the system by the H-bridge inverter unit. However, when the voltage passes through zero, the direction and magnitude of the current have different effects on the charging and discharging of the suspension capacitor voltage. In order to control the suspension capacitor voltage under different working modes, the charging and discharging of the capacitor voltage under different working modes is first analyzed.

[0108] The high-performance suspended capacitor H-bridge cascade multi-level inverter includes a zero-crossing comparison control method, which is: using the current inverter output voltage value u o Subtract the previous voltage value u olast , the difference is compared with the detected inverter output current i o If the polarity of the obtained signal is non-negative, the inverter is controlled to work in working mode 1, otherwise it works in working mode 2;

[0109] The working mode 1 is: when the inverter output voltage passes through the zero point in the positive half cycle, the current value i o ≤0, when p2(t)<0, the floating capacitor inverter unit absorbs active power, ic >0, the DC side floating capacitor of the floating capacitor inverter unit will work in the charging state; when p2(t)>0, the floating capacitor inverter unit outputs active power, i c <0, the DC side floating capacitor of the floating capacitor inverter unit is controlled to work in the discharge state;

[0110] When the voltage v o1 The output current value i at the zero crossing point in the positive half cycle o <0, the influence of the complementary region [α1, α2] on the voltage supply of the floating capacitor is shown in Figure 6(a). When the complementary region [α1, α2] remains unchanged, the average active power of the floating capacitor inverter unit is zero (P2 = 0); therefore, the floating capacitor will neither charge nor discharge; as shown in Figure 6(b), the complementary region [α1, α2] decreases, and the output current i o remains unchanged, the active power of the H-bridge increases, and the active power of the suspended capacitor inverter unit P2(t) is less than 0. In this case, the suspended capacitor absorbs energy and charges. Similarly, as shown in Figure 6(c), when the complementary area [α1, α2] increases, the active power of the suspended capacitor inverter unit P2(t) is greater than 0, so the suspended capacitor discharges.

[0111] The working mode 2 is: when the inverter output voltage passes through the zero point in the positive half cycle, the current value i o >0, when p2(t)<0, the floating capacitor inverter unit outputs active power, i c <0, the DC side floating capacitor of the floating capacitor inverter unit will work in the discharge state; when p2(t)>0, the floating capacitor inverter unit absorbs active power, i c >0, the DC side floating capacitor of the floating capacitor inverter unit will work in the charging state.

[0112] When the voltage v o1 The output current value i at the zero crossing point in the positive half cycle o When α1, α2 is greater than 0, the influence of the complementary area [α1, α2] on the voltage supply of the floating capacitor is similar to the above discussion. As shown in Figure 6(d), when the complementary area [α1, α2] remains unchanged, the floating capacitor will neither charge nor discharge. As shown in Figure 6(e), the complementary area [α1, α2] decreases and the floating capacitor discharges. As shown in Figure 6(f), when the complementary area [α1, α2] increases, the floating capacitor charges.

[0113] In order to achieve the above effects, a closed-loop control scheme of the capacitor voltage regulation system based on working mode switching is designed. Figure 7 As shown. First, the zero-crossing comparison program detects the current value when the inverter output voltage crosses the zero point in the positive half cycle. If the current value i o ≤0, using a given capacitor voltage reference value Vc *, with the actual value of the real-time sampling capacitor voltage V c Difference to get △V c , the duty cycle to be adjusted is obtained through the PI controller, thereby adjusting the output voltage of the H-bridge inverter unit and the active power. For example, when charging, △V c Increases, the instantaneous active power of the H-bridge inverter unit increases, the [α1, α2] area decreases, the switching frequency of the H-bridge inverter unit decreases, and the floating capacitor inverter unit outputs negative active power to control the charging of the floating capacitor voltage; on the contrary, when △V c When it decreases, the voltage of the floating capacitor is controlled to discharge; in this way, the actual value of the voltage of the floating capacitor can be controlled to tend toward the reference value.

[0114] If the output current value i o >0, the design control scheme is opposite to working mode 1. For example, when charging, △Vc decreases, the instantaneous active power of the H-bridge inverter unit decreases, the [α1, α2] area increases, the switching frequency of the H-bridge inverter unit increases, and the floating capacitor inverter unit outputs positive active power to control the charging of the floating capacitor; on the contrary, when △V c When the voltage increases, the floating capacitor of the floating capacitor inverter unit is controlled to discharge; thus, the voltage of the floating capacitor is controlled.

[0115] To sum up, the zero-crossing comparison program flow chart is as follows: Figure 8 This method uses the current inverter output voltage value u o Subtract the previous voltage value u olast , the difference is compared with the detected inverter output current i o If the polarity of the obtained signal is non-negative, the inverter is controlled to operate in the state of operating mode 1, otherwise it is controlled to operate in the state of operating mode 2.

[0116] (4) DC side double frequency power fluctuation suppression scheme

[0117] The high-performance suspended capacitor H-bridge cascade multi-level inverter also includes a third harmonic injection strategy based on a modulation wave decomposition modulation strategy: the control system can configure the proportional coefficient K p The negative feedback of the floating capacitor voltage forms a single closed loop to generate the power switch tube Q 11 , Q 12 , Q 13 , Q 14 , Q 21 , Q 22 , Q 23 , Q 24 PWM pulse signal; after injecting the third harmonic, v r1 'Decompose the modulation wave to get the decomposed H-bridge inverter unit modulation wave v r1and the suspended inverter unit modulated wave v r2 After injecting the third harmonic, the floating capacitor voltage is controlled by changing the active power of the H-bridge inverter unit.

[0118] For single-phase inverters, the double frequency power fluctuation on the DC side is an aspect that needs to be considered in the control of single-phase inverters. The third voltage harmonic is injected into the fundamental voltage, and the double frequency power generated by the fundamental voltage is redistributed. The oscillation power is absorbed by using a floating capacitor to suppress the double frequency power fluctuation on the DC side.

[0119] Assuming that the suspension capacitor voltage has a small AC component superimposed on it, the suspension capacitor voltage can be expressed as:

[0120] v c (t)=0.5V dc +V fc sin(2ωt-φ) (8)

[0121] Where V fc It is the amplitude of the double frequency ripple component on the floating capacitor voltage.

[0122] The double frequency power value generated by the third harmonic and the fundamental current is made equal to the secondary ripple power on the DC side to suppress the double frequency ripple.

[0123] Therefore, the instantaneous active power on the suspended capacitor can be calculated as:

[0124]

[0125] According to the power balance between the AC side and the DC side, it can be expressed as:

[0126] p ac (t) = p dc (t)+p C (t)(10)

[0127] Assuming the inverter conversion efficiency is 100%, its instantaneous input power P in Equal to the instantaneous output power P o , according to the triangular product and difference formula, we can get:

[0128]

[0129] In order to fully absorb the double frequency power fluctuation, the suspended capacitor voltage power p C (t) needs to be equal to the inverter double frequency power. Combining equations (10) and (11), let p C (t) is equal to the double frequency power fluctuation in equation (11), and it can be obtained that:

[0130]

[0131] Formula (12) proves the feasibility of using the suspended capacitor to absorb the double frequency power fluctuation to achieve DC voltage ripple suppression. In essence, it transfers the voltage ripple on the DC side capacitor voltage to the suspended capacitor on the suspended capacitor inverter unit. The suspended capacitor is located between the DC and AC sides of the inverter and can be used to buffer the fluctuating power and bear a certain voltage ripple. Therefore, if there is an AC component on the capacitor voltage, the double frequency power fluctuation can be absorbed by the suspended capacitor voltage. Therefore, by controlling the complementary conduction of the switch tubes on the same bridge arm of the suspended capacitor inverter unit and the synchronous conduction of the diagonally opposite power switch tubes, the four operating states of the suspended capacitor inverter unit can be obtained as follows:

[0132] It can be seen from Figure 9 that when the H-bridge inverter unit outputs current i H When the direction remains unchanged, there are different situations in which the floating capacitor is charged and discharged during a switching cycle:

[0133] 1. When i H When the floating capacitor inverter unit

[0134] ① As shown in Figure 9(a), the power switch device Q 21 and Q 24 conduction, and Q 22 and Q 23 In the off state, the floating capacitor inverter unit outputs the E level. In this case, the floating capacitor current of the floating capacitor inverter unit flows to the floating capacitor, and the floating capacitor is in a charging state. In the state of charging the floating capacitor, the double frequency power on the DC side of the H-bridge inverter unit is transferred to the floating capacitor through the floating capacitor inverter unit, and the voltage fluctuation across the DC side capacitor is reduced accordingly.

[0135] ②As shown in Figure 9(c), the power switch device Q 22 and Q 23 conduction, and Q 21 and Q 24 In the off state, the floating capacitor inverter unit outputs a -E level. In this case, the floating capacitor current of the floating capacitor inverter unit flows out of the floating capacitor, and the floating capacitor is in a discharging state.

[0136] 2. When i H When the current flows out of the floating capacitor inverter unit, similar to the above analysis, the following situations exist within one switching cycle

[0137] ① As shown in Figure 9(b), the power switch device Q 22 and Q 23 conduction, and Q 21 and Q 24In the off state, the floating capacitor inverter unit outputs -E level. In this case, the floating capacitor current of the floating capacitor inverter unit flows to the floating capacitor, and the floating capacitor is in a charging state. In the state of charging the floating capacitor, the double frequency power on the DC side of the inverter unit is transferred to the floating capacitor through the floating capacitor inverter unit, and the voltage fluctuation across the DC side capacitor is reduced accordingly.

[0138] ②As shown in Figure 9(d), the power switch device Q 21 and Q 24 conduction, and Q 22 and Q 23 In the off state, the floating capacitor inverter unit outputs the E level. In this case, the floating capacitor current of the floating capacitor inverter unit flows out of the floating capacitor, and the floating capacitor is in a discharging state.

[0139] In addition, the floating capacitor inverter unit has two operating modes that are neither charged nor discharged, as shown in Figure 9(e). At this time, the power switch device Q 21 and Q 22 conduction, and Q 23 and Q 24 In the off state, the floating capacitor inverter unit outputs 0 level. As shown in Figure 9(f), at this time, the power switch device Q 23 and Q 24 conduction, and Q 21 and Q 22 In the off state, the floating capacitor inverter unit outputs 0 level.

[0140] For the H-bridge inverter unit and the suspended capacitor inverter unit, unipolar frequency doubling modulation is used, and the modulation principle is shown in Figure 10 (a) and (b). The specific principle is to compare two complementary modulation waves with the same triangular carrier, and the obtained pulses act on different power switching devices respectively. Every time a driving pulse is issued, the output levels of the two H-bridge units change twice, and the final equivalent switching frequency of the power device is 2 times the actual switching frequency. The power switch tube in the unipolar frequency doubling modulation strategy has a faster switching state change speed than the power switch tube in the unipolar modulation strategy, which can double the output voltage change speed of the inverter.

[0141] In the actual process, after the third harmonic is injected, the modulation wave changes, which will change the overmodulation interval of the suspended capacitor inverter unit. From the above analysis, after the third harmonic is injected, the output voltage amplitude v of the suspended capacitor inverter unit at the conduction angle α can be calculated. α- and v α+ for:

[0142] v α- =V m sin(α)-kV msin(3α) (13)

[0143] v α+ =V dc -V m sin(α)+kV m sin(3α) (14)

[0144] In order to prevent the suspended inverter unit from overmodulation, v α- and v α+ It should not exceed the voltage value of the floating capacitor, k is the injected third harmonic content, and m is the modulation index. Therefore, when the input DC voltage value and modulation index are determined, the k value when no overmodulation occurs can be calculated by the above formula, and the relationship between m and k is plotted as follows: Fig.11 shown.

[0145] Depend on Fig.11 It can be seen that with the increase of the modulation index m, the injected third harmonic content k value first decreases, then increases, and then decreases. Since the injected third harmonic should satisfy k value ≤ 1, only when the m value is within a certain range can the k value ≤ 1 be satisfied. When m = 0.29, theoretically, the double frequency content can be suppressed by up to 97%. Although the voltage ripple is small after suppression, due to the modulation index m ≤ 0.33, the inverter output level number is only three levels, which loses the advantage of outputting more levels.

[0146] The present invention proposes a third harmonic injection strategy based on the modulation wave decomposition modulation strategy. Fig.12 As shown, the entire control system can be configured by the proportional coefficient K p The negative feedback of the floating capacitor voltage forms a single closed loop to generate the power switch tube Q 11 , Q 12 , Q 13 , Q 14 , Q 21 , Q 22 , Q 23 , Q 24 PWM pulse signal. After injecting the third harmonic, v r1 'Decompose the modulation wave to get the decomposed H-bridge inverter unit modulation wave v r1 and the suspended inverter unit modulated wave v r2 After injecting the third harmonic, the floating capacitor voltage is controlled by changing the active power of the H-bridge inverter unit.

[0147] The high-performance suspended capacitor H-bridge cascade multi-level inverter, the suspended capacitor voltage control method is: using a proportional controller, giving a capacitor voltage reference value V c *, with the actual value of the real-time sampling capacitor voltage V c Difference to get △V c, the duty cycle to be adjusted is obtained through the proportional controller, thereby adjusting the output voltage of the H-bridge inverter unit; when charging, △V c Increase, the floating capacitor inverter unit outputs negative active power to control the floating capacitor voltage charging; conversely, when △V c When it decreases, the suspension capacitor voltage is controlled to discharge; by repeating this process, the actual value of the suspension capacitor voltage can be controlled to tend toward the reference value.

[0148] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A high-performance floating capacitor H-bridge cascade multi-level inverter, characterized by: The inverter includes an H-bridge inverter unit, a floating capacitor inverter unit, an output filter inductor L1 and an output filter capacitor C1; the H-bridge inverter unit consists of four switch tubes Q 11 , Q 12 , Q 13 and Q 14 Connected into a bridge circuit, its input side is connected to the DC voltage source V dc The floating capacitor inverter unit consists of 4 switch tubes Q 21 , Q 22 , Q 23 , Q 24 It is connected to the floating capacitor C to form a bridge circuit, whose input side is connected to the output side of the H-bridge inverter unit, and its output side is connected to the load through the output filter inductor L1 and the output filter capacitor C1.

2. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 1, characterized in that: The suspension capacitor C is located between the DC and AC sides of the suspension capacitor inverter unit and can be used to buffer fluctuating power and bear a certain voltage ripple. The voltage value of the suspension capacitor C is V c is the DC voltage source V dc Half the voltage value.

3. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 1, characterized in that: The inverter has multiple conduction modes, which form 8 working modes. The 8 working modes are: The working modes when the positive half cycle outputs 2E, E, and 0 include working modes 1-4: Working mode 1: The floating capacitor H-bridge cascade multi-level inverter outputs 2E level; at this time, the H-bridge inverter unit switch tube Q 11 , Q 14 When the H-bridge inverter unit is turned on, it outputs 2E level. When the suspended inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 21 , Q 22 When it is turned on, the floating capacitor inverter unit outputs 0 level, and the capacitor is neither charged nor discharged; Working mode 2: The floating capacitor H-bridge cascade multi-level inverter outputs E level; at this time, the H-bridge inverter unit switch tube Q 11 , Q 14 The H-bridge inverter unit outputs 2E level; the switching tube Q of the floating inverter unit is turned on. 22 , Q 23 When the inverter is turned on, the floating inverter unit outputs -E level. When the inverter output current direction is positive, the capacitor is charged, and when the inverter output current direction is negative, the capacitor is discharged. Working mode 3: The floating capacitor H-bridge cascade multi-level inverter outputs E level; There are two switching action modes when the H-bridge inverter unit outputs 0 level. In this working mode, the switching action mode is Q 11 , Q 12 The H-bridge inverter unit outputs 0 level; the suspended inverter unit outputs E level, and the suspended inverter unit switch tube Q 21 , Q 24 When the inverter is turned on and the output current direction is positive, the capacitor is discharged, and when the output current direction is negative, the capacitor is charged; Working mode 4: The floating capacitor H-bridge cascade multi-level inverter outputs 0 level; The H-bridge inverter unit and the suspended inverter unit both output 0 level. In this working mode, the switch tube of the H-bridge inverter unit is Q 11 , Q 12 Conducting, suspending the inverter unit switch tube Q 21 , Q 22 When conducting, the capacitor neither charges nor discharges; The working modes when the negative half cycle outputs 2E, E, and 0 include working modes 5-8: Working mode 5: The floating capacitor H-bridge cascade multi-level inverter outputs -2E level; at this time, the H-bridge inverter unit switch tube Q 12 , Q 13 When the H-bridge inverter unit is turned on, it outputs -2E level. When the suspended inverter unit outputs 0 level, there are two switching action modes. In this working mode, the switching action mode is Q 23 , Q 24 When it is turned on, the floating capacitor inverter unit outputs 0 level, and the capacitor is neither charged nor discharged; Working mode 6: The floating capacitor H-bridge cascade multi-level inverter outputs E level; at this time, the H-bridge inverter unit switch tube Q 12 , Q 13 The H-bridge inverter unit outputs -2E level; the switching tube Q of the floating inverter unit is turned on. 21 , Q 24 When the inverter is turned on, the suspended inverter unit outputs E level. When the inverter output current direction is positive, the capacitor is charged, and when the inverter output current direction is negative, the capacitor is discharged. Working mode 7: floating capacitor H-bridge cascade multi-level inverter output -E level; There are two switching action modes when the H-bridge inverter unit outputs 0 level. In this working mode, the switching action mode is Q 13 , Q 14 The H-bridge inverter unit outputs 0 level; the suspended inverter unit outputs -E level, and the suspended inverter unit switch tube Q 22 , Q 23 When the inverter is turned on and the output current direction is positive, the capacitor is discharged, and when the output current direction is negative, the capacitor is charged; Working mode 8: The floating capacitor H-bridge cascade multi-level inverter outputs 0 level; The H-bridge inverter unit and the suspended inverter unit both output 0 level. In this working mode, the switch tube of the H-bridge inverter unit is Q 13 , Q 14 Conducting, suspending the inverter unit switch tube Q 23 , Q 24 When the capacitor is turned on, it neither charges nor discharges.

4. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 1, characterized in that: The inverter also includes a hybrid frequency modulation strategy based on modulation wave decomposition. The strategy targets the overmodulation of the E level by adding a modulation process in this interval, decomposing the modulation wave of the suspended capacitor inverter unit that exceeds the carrier portion, and at the same time adjusting the modulation waves of the overmodulation portions of the H-bridge inverter unit and the suspended capacitor inverter unit, so that the H-bridge inverter unit outputs 2E and 0 levels, and the suspended capacitor unit outputs -E and E levels, thereby achieving normal E level output.

5. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 4, characterized in that: The specific working mode of the hybrid frequency modulation strategy based on modulation wave decomposition is: the H-bridge inverter unit operates at high frequency using a unipolar frequency multiplication modulation method with modulation wave inversion in the decomposition interval, and the switch tube Q 11 and Q 12 Using a modulated wave signal with equal amplitude but 180° phase difference, v ref1- It is the inverted modulation wave. In any carrier cycle, the switch tube Q 11 and Q 12 The modulated wave signal and the carrier wave have two intersection points: when v ref1 ≥U cH When the switch tube Q 11 On, on the contrary Q 13 When V ref1- ≥U cH When the switch tube Q 12 On, on the contrary Q 14 conduction.

6. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 4, characterized in that: The specific working mode of the hybrid frequency modulation strategy based on modulation wave decomposition is: the floating capacitor inverter unit adopts single polarity frequency multiplication modulation in all intervals, and the switch tube Q 21 and Q 22 Use a modulated wave signal v with equal amplitude but 180° phase difference ref2 and v ref2- ; When the sine wave v ref >0, Q 11 is high level, and low level at other times; when u m >u c2 When Q 12 is low level, and Q 12 is high level; when u m >u c1 When Q 21 is high level, and Q 21 is low level; when u m >u c2 When Q 22 is high level, and Q 22 The output voltage waveform of the modulation wave of the suspended capacitor inverter unit after the modulation wave is decomposed is v2 ’ .

7. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 1, characterized in that: The inverter also includes a capacitor voltage regulation system control strategy based on working mode switching; the strategy is: by introducing the load end output voltage v o1 , output current i o , floating end capacitor voltage V c and the capacitor voltage reference value V c *Perform zero-crossing comparison, and control the output value △V c After the kp link, the output part v' of the H-bridge inverter unit during high-frequency conversion is obtained. v' and v a The given values ​​are added to get the modulation wave v of the H-bridge inverter unit ref1 , modulation wave v ref1 The modulation circuit is used to modulate the four switch tubes Q of the floating capacitor inverter unit. 21 , Q 22 , Q 23 , Q 24 Modulate.

8. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 7, characterized in that: The inverter includes a zero-crossing comparison control method, which is: using the current inverter output voltage value u o Subtract the previous voltage value u olast , the difference is compared with the detected inverter output current i o If the polarity of the obtained signal is non-negative, the inverter is controlled to work in working mode 1, otherwise it works in working mode 2. The working mode 1 is: when the inverter output voltage passes through zero in the positive half cycle, the current value i o ≤0, when p2(t)<0, the floating capacitor inverter unit absorbs active power, i c >0, the DC side floating capacitor of the floating capacitor inverter unit will work in the charging state; when p2(t)>0, the floating capacitor inverter unit outputs active power, i c <0, the DC side floating capacitor of the floating capacitor inverter unit is controlled to work in the discharge state; The working mode 2 is: when the inverter output voltage passes through zero in the positive half cycle, the current value i o >0, when p2(t)<0, the floating capacitor inverter unit outputs active power, i c <0, the DC side floating capacitor of the floating capacitor inverter unit will work in the discharge state; when p2(t)>0, the floating capacitor inverter unit absorbs active power, i c >0, the DC side floating capacitor of the floating capacitor inverter unit is controlled to work in the charging state.

9. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 1, characterized in that: The inverter also includes a third harmonic injection strategy based on the modulation wave decomposition modulation strategy: the control system can configure the proportional coefficient K p The negative feedback of the floating capacitor voltage forms a single closed loop, generating a power switch tube Q 11 , Q 12 , Q 13 , Q 14 , Q 21 , Q 22 , Q 23 , Q 24 PWM pulse signal; after injecting the third harmonic, v r1 'Decompose the modulation wave to get the decomposed H-bridge inverter unit modulation wave v r1 and the suspended inverter unit modulation wave v r2 After injecting the third harmonic, the floating capacitor voltage is controlled by changing the active power of the H-bridge inverter unit.

10. The high-performance floating capacitor H-bridge cascade multi-level inverter according to claim 9, characterized in that: The suspension capacitor voltage control method is: using a proportional controller, giving a capacitor voltage reference value V c *, and the actual value of the real-time sampling capacitor voltage V c Take the difference to get △V c , the duty cycle to be adjusted is obtained through the proportional controller, thereby adjusting the output voltage of the H-bridge inverter unit; when charging, △V c Increase, the floating capacitor inverter unit outputs negative active power to control the floating capacitor voltage charging; On the contrary, when △V c When it decreases, the voltage of the floating capacitor is controlled to discharge; by repeating this process, the actual value of the floating capacitor voltage can be controlled to tend to the reference value.

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